Author Correction: Grazing enhances species diversity in grassland communities.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Grazing enhances species diversity in grassland communities.

In grassland studies, an intermediate level of grazing often results in the highest species diversity. Although a few hypotheses have been proposed to explain this unimodal response of species diversity to grazing intensity, no convincing explanation has been provided. Here, we build a lattice model of a grassland community comprising multiple species with various levels of grazing. We analyze the relationship between grazing and plant diversity in grasslands under variable intensities of grazing pressure. The highest species diversity is observed at an intermediate grazing intensity. Grazers suppress domination by the most superior species in birth rate, resulting in the coexistence of inferior species. This unimodal grazing effect disappears with the introduction of a small amount of nongrazing natural mortality. Unimodal patterns of species diversity may be limited to the case where grazers are the principal source of natural mortality.

A power law model for analyzing spatial patterns of vegetation abundance in terms of cover, biomass, density, and occurrence: derivation of a common rule.

The cover, biomass, density, and frequencies of occurrence of individual species are important measures for characterizing plant communities. Examination of the statistical properties of vegetation data obtained through a quadrat survey provides insight into the spatial structure of plant communities and plant species diversity. In community analysis, we assume that x is theoretical variance calculated under the assumption that the abundance of a species follows a random distribution among quadrats (which we can obtain easily), and y is quadrat-to-quadrat variance calculated based on the observed data for a species. If the relationship y = Axb or logy = logA + blogx holds for two measurable traits of the plant community, x and y, the relationship is referred to as the power law, where A and b are constants. Then, an ideal index for measuring the spatial heterogeneity (δ) of the vegetation variable for each species was defined as δ = logy - logx. If δ = 0, the spatial heterogeneity of the species is random; if δ > 0, the heterogeneity exceeds a random pattern; and if δ < 0, the heterogeneity is less than a random pattern. In previous works in 2001 and 2014, we demonstrated that using the power law based on occurrence and density is a valuable approach to vegetation surveys and analyses. In this paper, the power law is mathematically extended and practical evidence is given for its application to cover and biomass of each species within a plant community. All measurements of cover, biomass, density, and frequency of occurrences were fitted to the power law, and plots of δ against the abundance values of these variables for each species in the community well described abundance and spatial pattern of each species in the environment. The power law is applicable not only to small-scale quadrats such as 50 × 50 cm but also to large-scale vegetation maps obtained using remote sensing and aerial photographic techniques.

Anthropogenic effects on a tropical forest according to the distance from human settlements.

The protection of tropical forests is one of the most urgent issues in conservation biology because of the rapid deforestation that has occurred over the last 50 years. Even in protected forests, the anthropogenic effects from newly expanding villages such as harvesting of medicinal plants, pasturing cattle and forest fires can induce environmental modifications, especially on the forest floor. We evaluated the anthropogenic effects of the daily activities of neighboring residents on natural forests in 12 plots extending from the village boundary into a natural forest in Thailand. The basal area per unit land area did not present a significant trend; however, the species diversity of woody plants decreased linearly towards the village boundary, which caused a loss of individual density because of severe declines in small saplings compared with adult trees and large saplings in proximity to the village. An analysis of tree-size categories indicates a lack of small samplings near the village boundary. The current forest appears to be well protected based on the adult tree canopy, but regeneration of the present-day forests is unlikely because of the loss of seedlings.

(134)Cs and ¹³7Cs levels in a grassland, 32 km northwest of the Fukushima 1 Nuclear Power Plant, measured for two seasons after the fallout.

We measured the levels of radioactive caesium (RACs; ¹³4Cs and ¹³7Cs) in plants and soil in a grassland, 32 km northwest of the Fukushima 1 Nuclear Power Plant, from June 2011 to October 2012. In 2011, the highest RACs levels (¹³4Cs + ¹³7Cs) in plants and in the 0-5 cm soil layer were approximately 80 kBq per kg dry weight (DW). Forage grasses and clovers in this grassland showed similar RACs levels. On a DW basis, the levels of RACs in these plants tended to increase with increasing biomass over both years, but the absolute levels decreased in 2012. The RACs levels in the soil decreased sharply with soil depth; the RACs level in the 5-10 cm soil layer was only 3 % of that in the 0-5 cm layer. The transfer factor (ratio of radioactivity in plant parts on DW basis to that in the 0-10 cm soil layer) was 0.5 and 1.0 for the aboveground and belowground plant parts, respectively, in 2011, and these values decreased by approximately 50 % in 2012. We discuss the possible mechanisms underlying these trends, and strategies to decrease the level of RACs in plants to the permissible level for forage.

Temporal changes in testis weight during the past 50 years in Japan.

The ever-increasing presence of environmental toxicants and their disruptive effect on the reproductive systems of wildlife raises the question of possible damage to the human reproductive system. Using medicolegal data from over 20,000 Japanese men subjected to necropsy from 1948 to 1998, we investigated temporal changes in testis weight to find possible evidence of male reproductive disorders. We also carried out a histological examination of 747 testes collected from 1978 to 1998. Our detailed analyses of the development of testis weight over the past 50 years have revealed four clear phenomena: (i) the age at which testis weight reaches its maximum has decreased; (ii) peak weight showed a general increase until it started to decline in boys born after 1960; (iii) the decline-rate at which testis weight decreases after its peak has greatly accelerated; and (iv) the onset of increasing testis weight of boys has occurred at a progressively younger age. Our quantitative analyses of testis weight indicate the possibility of a subtle reproductive disorder in Japanese men, especially in those born after 1960. Together with the accelerated development and decline in testis weight during the past 50 years, the decline in peak weight might be indicative of a subtle interference of environmental toxicants with male reproductive organogenesis.